1. Field of the Invention
The present invention relates to a disk cartridge in which a disk-like magnetic medium is held in a casing which is formed by combining upper and lower half casings.
2. Discussion of Background
Floppy disks have widely been used as exchangeable information storage media which can be fitted to or removed from a magnetic recording/reproducing device for storage or transportation in the same manner as magnetic tape cassettes and disk packs. However, so-called 8-inch or 5-inch floppy disks, which have been generally used, have disadvantages that the mechanical strength of the casing is poor and dust easily enters into the inside of the casing.
In 3.5-inch floppy disks, the above-mentioned disadvantages are eliminated by the measures that a casing formed by combining upper and lower half casings made of a resinous material is used, a shutter is provided at the magnetic head insertion window formed in either or both half casings, and a hub formed in a magnetic disk is opposed to a magnetic disk driving window, the magnetic disk being held in the casing in a rotatable manner.
FIG. 8 is a diagram of a conventional disk cartridge mounted on a magnetic recording/reproducing device, the diagram corresponding to a cross-sectional view taken along a line A--A in FIG. 6. In FIG. 8, a reference numeral 10 designates a disk cartridge of a hard casing which is formed by combining upper and lower half casings 12, 14, in which a magnetic disk (not shown) attached with a hub at its central portion is rotatably received, and a numeral 16 designates a driving shaft of the magnetic recording/reproducing device, which extends into the central opening of the hub to be connected with it. A reference numeral 18 designates a position-determining annular rib which defines a rotating region for the hub, the annular rib being formed at the central portion of the inner surface of the upper half casing 12 as a base plate, and a numeral 20 designates a magnetic disk driving window formed at the central portion of the lower half casing 14 as a base plate.
The detail of the construction of each of the inner surface of the upper and lower half casings 12, 14 will be described with reference to FIGS. 6 and 7. As is clear from FIG. 6, the position-determining annular rib 18 is in a continuous circle form, and the annular rib 18 is adapted to bear the end of the driving shaft 16 at its center of the region surrounded by the continuous circular rib 18. Outside the annular rib 18, arched walls 22, 24 are concentrically arranged and a circle formed by the both arched walls faces the magnetic disk and the hub, and forms a rotating region for them. A magnetic head insertion window 26 opens at the rotating region of the magnetic disk. A plurality of rod-like hubs 28 project vertically from the inner surface of the upper half casing 12 at a position corresponding to a lifter.
As is clear from FIG. 7, the shape of the magnetic disk driving window 20 is circular, and the inner diameter of the window is slightly larger than the outer diameter of the annular rib 18 and formed in a concentric manner. At a radially outer portion of the magnetic tape driving window 20, arched walls 30, 32 which oppose the arched walls 22, 24 of the upper half casing 12 project. A magnetic head insertion window 34 is formed in the lower half casing at the rotating region of the magnetic disk. A plurality of ribs 36 are also formed on the inner surface of the lower half casing so as to be used for fixing the lifter.
In use of the conventional disk cartridge 10, when the cartridge 10 is mounted on a magnetic recording/reproducing device, the top of the driving shaft 16 comes in contact with the central portion of the inner surface of the upper half casing 12 so as to push it up, whereby the upper half casing 12 is deformed by an upwardly projecting force by the driving shaft 16. The deformation rather takes place at a portion outside the annular rib 18 for determining the position of the hub. It is because the annular rib 18 continuously surrounds that area having its center to which the end portion of the driving shaft 16 contacts, and the central area of the upper half casing is hardly deformed because of its having a large rigidity. Accordingly, the deformation mostly occurs at the outer circumferential portion of the upper half casing 12, this causing deformation in the lower half casing 14 by the influence of the deformation in the upper half casing 12. Since the lower half casing 14 has reference holes 38, 40 at its outer circumferential portion of the base plate which are used for determining the position of the disk cartridge 10 to the magnetic recording/reproducing device. Therefore, the deformation of the lower half casing 14 can not determine the correct position and prohibits normal recording/reproducing operations.